Apparatus and method for producing oil and gas using buoyancy effect

ABSTRACT

A method of producing oil and gas from a gathering manifold or a well. The method includes the steps of channeling field production into a sealed vessel through an inlet pipe, and permitting oil and gas components of the field production to separate naturally from water and other fluids within the vessel. The method further includes the steps of evacuating the separated oil and gas from the vessel via pipelines attached to the vessel at locations corresponding to the separated oil and gas, and pumping seawater into the vessel to pressurize the vessel and thereby aid in the production of oil and gas from the vessel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/495,929, filed on Sep. 25, 2014, which claims priority to and thebenefit of U.S. Provisional Application No. 61/884,724, filed on Sep.30, 2013, the full disclosures both of which are hereby incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present technology relates to oil and gas production. In particular,the present technology relates to oil and gas production from subseagathering manifolds or wells using buoyancy.

2. Description of the Related Art

The production of oil and gas from subsea gathering manifolds or oilwells typically requires raising crude oil through a riser from theseabed to the sea surface. This procedure has inefficiencies, including,for example, pressure drop within the riser. This pressure dropincreases when the crude oil pressure falls below the bubble point,which changes the flow from a single-phase to a two-phase flow.

In addition, separation of oil and gas from crude oil is typicallycarried out at an onshore gas oil separation plant. This requires, afterthe crude oil reaches the platform through the risers, multiphase pumpsto ship the crude oil to the onshore plant. Accordingly, an oil producermust invest in expensive equipment, such as oil pumps and gascompressors, and gas oil separation plants.

SUMMARY OF THE INVENTION

The present technology provides a method of producing oil and gas from asubsea gathering manifold or well. The method includes the steps ofchanneling field production into a sealed, partially submerged, and/orseawater-filled vessel through an inlet pipe, and permitting oil and gascomponents of the field production to separate naturally from water andother fluids within the vessel. The method also includes evacuating theseparated oil and gas from the vessel via pipelines attached to thevessel at locations corresponding to the separated oil and gas, andpumping seawater into the vessel to pressurize the vessel and therebyaid in the production of oil and gas from the vessel.

In some embodiments, the method can further includes lowering thepressure in the vessel to allow for gas to gather to the top of thevessel. In addition, the step of stopping the introduction of seawaterinto the vessel before the vessel reaches a minimum allowable pressureof the inlet pipe can be included.

In other embodiments, the method can include insulating or heating thevessel to reduce cooling of the vessel to minimize the formation ofhydrates within the vessel, as well as adding anti-hydrate additives tothe seawater pumped into the vessel to further minimize the formation ofhydrates within the vessel. Furthermore, the method can include limitingthe flow rate of seawater pumped into the vessel to reduce emulsion ofthe seawater with oil in the vessel.

The present technology also provides a method of installing a gas andoil production vessel at an offshore gathering manifold or well site.The method includes towing the vessel to an offshore manifold or a wellsite with a ship, tilting the vessel into an upright position, with thetop of the vessel oriented above the bottom of the vessel, and partiallyfilling the vessel with seawater until the vessel is partiallysubmerged. In addition, the method includes fixing the vessel to theseabed using pillars or cables, or a combination of pillars and cables,connecting a pipe from the gathering manifold or well to the bottom ofthe vessel to deliver field production to the vessel, connectingproduction pipes at predetermined locations on the vessel for flowingoil and gas away from the vessel, connecting pumps to the vessel to pumpseawater into the vessel for purposes of pressurizing the vessel.

In certain embodiments, the method can include the step of releasing airfrom an upper portion of the vessel as seawater enters the vessel, aswell as filtering the seawater as it enters the vessel to preventcontaminates from entering the vessel. In addition, the method caninclude attaching air-filled spheres to the vessel using cables, theair-filled spheres designed to float on the sea surface to help supportthe vessel, as well as pumping seawater into the vessel to evacuateremaining air from the vessel, and to pressurize the oil and gas withinthe vessel.

The present technology also provides a system for bringing produced oiland gas from a subsea gathering manifold or a wellhead to a sea surface.The system includes a vessel containing seawater, and extending from asubsea position to the sea surface, as well as an inlet pipe attached tothe bottom of the vessel to deliver produced oil and gas from the subseawellhead to the bottom of the vessel, so that the oil, gas, and water iscombined inside the vessel and allowed to naturally separate inside thevessel. Furthermore, the system includes a pump attached to the vesselto pump water into the vessel to pressurize the vessel, and at leastfirst, second, and third pipes attached to the vessel at predeterminedlocations to pull fluids from the vessel, the first pipe attached to anupper portion of the vessel to collect gas that has separated to theupper portion of the vessel, the second pipe attached to a centralportion of the vessel to collect oil that has separated to the centralportion, between the gas and the seawater; and the third pipe attachedto a lower portion of the vessel to collect seawater that has separatedto the lower portion of the vessel.

In some embodiments of the technology, the vessel can be sealed tomaintain a desired pressure, and insulated to control temperature.Furthermore, the vessel can be tapered, having a larger cross section ata lower end and a smaller cross-section at an upper end, therebyconcentrating oil and gas to concentrate in the upper portions of thevessel for ease of production. In addition, the system can furtherinclude filters attached to the vessel or the pump to filter seawaterbeing pumped into the vessel, and a scraper in the vessel to scrape thebottom of the vessel and clear the bottom of the vessel of resins orasphaltenes that may collect on the bottom of the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technology will be better understood on reading thefollowing detailed description of nonlimiting embodiments thereof, andon examining the accompanying drawings, in which:

FIG. 1 is a side schematic view of an oil and gas production systemaccording to an embodiment of the present technology;

FIG. 2 is a side schematic view of the oil and gas production systemshown in FIG. 1;

FIG. 3 is a side schematic view of an oil and gas production systemaccording to an alternate embodiment of the present technology;

FIG. 4 is a side schematic view of an oil and gas production systemaccording to yet another embodiment of the present technology;

FIG. 5 is a side schematic view of a step in a method of installing andusing the system of FIG. 1;

FIG. 6 is a schematic view of another step in a method of installing andusing the system of FIG. 1;

FIG. 7 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 8 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 9 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 10 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 11 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 12 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 13 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 14 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 15 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 16 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 17 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 18 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 19 is a side schematic view of another step in a method ofinstalling and using the system of FIG. 1;

FIG. 20 is a side cross-sectional view of a vessel for collecting oiland gas, and including a scraper;

FIG. 21 is a side schematic view of an alternate embodiment of a systemfor producing oil and gas;

FIG. 22 is a two dimensional representation of a model reservoiraccording to an embodiment of the present technology;

FIG. 23 is a three dimensional representation of the model reservoir ofFIG. 22;

FIG. 24 is a chart showing the total reservoir production rate fordifferent models representing embodiments of the present technology; and

FIG. 25 is a chart showing total cumulative production for differentmodels represented in FIG. 24.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The foregoing aspects, features, and advantages of the presenttechnology will be further appreciated when considered with reference tothe following description of preferred embodiments and accompanyingdrawings, wherein like reference numerals represent like elements. Indescribing the preferred embodiments of the technology illustrated inthe appended drawings, specific terminology will be used for the sake ofclarity. However, the embodiments are not intended to be limited to thespecific terms used, and it is to be understood that each specific termincludes equivalents that operate in a similar manner to accomplish asimilar purpose.

The technology disclosed herein includes a method that utilizes buoyancyto help produce oil and/or gas production from the seabed to a seasurface. In one example embodiment, as described in detail below, oiland gas is gathered in a production manifold, and then released into thebottom of a vessel that is filled with seawater. This sealed vessel canhave many beneficial characteristics. For example, it can be sealed,insulated, and/or temperature controlled. Furthermore, the sealed vesselcan replace other structures, such as production risers, offshoreproduction platforms, and gas oil separation systems.

In certain embodiments, the sealed vessel can stretch from the seabed tothe sea surface. It can be anchored to the seabed by metallic pillars orother appropriate mechanism, and is can have connected to it floatingspheres that reach the sea surface, thereby serving to mark the positionof the vessel. Within the vessel, the produced materials, after leavingthe well and entering the vessel, separate into their individualcomponents, such as oil, gas, and water. These components are permittedto separate naturally, based on the principle of buoyancy, with the oilrising above the water within the vessel.

To understand how the vessel of the present technology functions, it isnecessary to understand the principle of buoyancy. Buoyancy is an upwardforce exerted by a surrounding fluid on an immersed object. According toArchimedes law, the value of a buoyant force is equal to the weight ofthe fluid the object displaces. Thus the net force exerted on a fully orpartially immersed object becomes the summation of its weight(downward), overburden pressure (downward), and the buoyancy force(upward). The buoyant force is governed by the following equations:

F _(Net) =−M _(Object) *C _(g) −P _(OB) +F _(Buoyancy)

F _(Net) =−V _(Object)*ρ_(Object) *C _(g) −P _(OB) +V_(Object)*ρ_(Displaced Fluid) *C _(g)

F _(Net) =V _(Object) *C _(g)(ρ_(Displaced Fluid)−ρ_(Object))−P _(OB)

In these equations, the symbols have the following meanings:

F_(Net)=Net Force

M_(Object)=Object Mass

C_(g)=Gravitation Acceleration Constant

P_(OB)=Overburden Pressure

F_(Buoyancy)=Buoyancy Force

ρ_(Object)=Object Density

ρ_(Displaced Fluid)=Displaced Fluid Density

When the difference between the object and the fluid densities is largeenough to overcome the overburden pressure, the object raises upward.The immersed object can be solid, liquid, or gas.

In the present technology, the buoyancy principle acts to raise crudeoil to the top of the vessel, which causes a reduction in cride oil'spressure that leads to separating dissolved gas from crude oil, forminga distinct gas phase on top, oil phase in the middle, and water phase atthe bottom. For example, oil and gas are immiscible with seawater at thesea bottom conditions. Therefore, oil and gas form a continuousdistinctive phase. Furthermore, at the bottom of the sea, seawater iscold and dense. On the other hand, crude oil is produced at a relativelyhigher temperature, and is typically lighter in density than seawater.Accordingly, if crude oil and gas is mixed with seawater, the mixturewill naturally settle out into individual layers of gas, oil, and water.

As desired by an operator, the individual components can then beextracted from the vessel. For example, gas can be produced from the topof the vessel (although a calculated amount of gas can be kept withinthe vessel for purposes of pressure control, if needed). Similarly, oilcan be produced from a point at the side of the vessel corresponding tothe level of the oil within the vessel. All other produced fluids,including water, can be produced from a lower point at the side of thevessel corresponding to the level of such fluids in the vessel. Tomaintain the desired vessel pressure, thereby maintaining the ability toeffectively produce fluids from the vessel, ambient seawater can bepumped into the vessel. Such ambient seawater can be heated and/orfiltered if desired.

Using the vessel shown and described herein, ships can receive oildirectly from the vessel, and no longer have to rely on onshoreseparation facilities. Therefore, the vessel of the present technologycan save the energy used to ship crude oil (through pipes or ships) toonshore gas and oil separation plants (GOSPs) for separation. Further,the method herein disclosed has the advantages of reducing capital andoperating costs, extending the life of offshore reservoirs, being safeand environmentally sound, and being capable of being applied at anystage of production, even after abandonment of a reservoir or a well.

Referring now to FIG. 1, there is shown one embodiment of the presenttechnology that utilizes buoyancy to deliver oil and gas production fromthe seabed to a sea surface. For example, in the embodiment shown,gathered field production is released from a vertical pipe 10, attachedto a wellhead or a group of wellheads via a gathering manifold (notshown) into the bottom of a vessel 12. The vessel 12 is filled withseawater. The vertical pipe 10 is itself connected to a flowline comingfrom a well or a group of wells via a gathering manifold. In certainembodiments, the vessel 12 can be sealed, insulated, and potentiallytemperature controlled. In addition, the vessel 12 can stretchvertically form the seabed to the sea surface, and can taper from alarger diameter toward the seabed to a smaller diameter toward the seasurface. In some cases, such as where a reservoir is an ultra-deepoffshore reservoir, a vessel 12 may not be able to extend from theseabed to the sea surface. In such a case, the vertical pipe 10 could beincreased in length to compensate for the vessel 12 vertical lengthshortage, as shown in FIG. 21.

Inside the vessel 12, oil and gas rise to the top of the vessel 12 bybuoyancy. During this rise, oil, gas, and formation water naturallyseparate. After separation, and as shown in FIG. 2, gas 14 rises to thetop of the vessel 12, oil 16 rises to a midpoint in the vessel 12, andall other produced fluids 18, mixed with seawater in the vessel 12, arecollect at the bottom of the vessel 12. As shown in FIG. 2, flowline 20,which may be, for example, pipes, connect to the vessel 12 at selectivelocations to pipe either the gas 14, oil 16, or other produced fluids 18away from the vessel 12. As oil and gas enters the vessel 12, and issubsequently piped out of the vessel 12, the pressure within the vessel12 can be maintained by pumping, or otherwise allowing the ingress of,ambient seawater (which could also be heated), into the sides of thevessel when needed. Seawater can be subjected to filtration prior tobeing pumped into the vessel 12.

Although the shape of the vessel 12 is shown in FIGS. 1 and 2 to beconical, the vessel 12 can be any appropriate shape. Tapered shapes,however, such as that of FIGS. 1 and 2, can be advantageous because theyallow faster response of the Oil Water Line (OWL) and the Gas Oil Line(GOL) to injected water. Tapered shapes also allow significant volumesof oil and gas to be collected at or near the top of the vessel 12,which leads to expedited production. In addition, the tapered shapefocuses the buoyant force on a smaller area, thus increasing themagnitude of the upward pressure force that the oil and gas exerts onthe top of the vessel 12. This upward pressure force can help reducesthe overall weight of the vessel on pillars 22 used to support thevessel 12 at the sea floor. Alternative shapes to the conical vessel 12of FIGS. 1 and 2 could include, for example, a spherical vessel 12(shown in FIG. 3), or a vessel 12 having an elliptical cross-section(shown in FIG. 4).

The technology disclosed herein could help in boosting oil and gasproduction from the vessel. For example, at initial stages of theproduction procedure, pressure can be intentionally lowered in thevessel to allow for a gas cap to form at the top. Then, seawaterinjection can begin, which increases pressure at the vessel up to thedesired pressure level. Thereafter, the oil valve can be opened, andpressurized oil is evacuated from the vessel 12. Preferably, seawaterinjection stops when, or before, the vessel 12 reaches the minimumallowable pressure of the inlet pipe 10 at the bottom of the vessel 12.

In some embodiments, the vessel 12 can be insulated and/or temperaturecontrolled. This is beneficial because gas can form hydrates in highpressure and low temperature environments. Insulating and maintainingthe internal temperature of the vessel at appropriate levels can helpprevent hydrates from forming. In addition, anti-hydrates additives canbe added to the injected seawater as an added precaution.

In some embodiments, there can be a limit on the injected seawater flowrate. If the injected seawater enters the vessel 12 at too high a flowrate, it could create emulsion with produced oil. When emulsion forms,oil particles become suspended in water. In such a scenario, there wouldnot be a distinctive OWL. Such a limit on injected sea water flow ratecan be accomplished, for example, through the use of valves 31 on thepumps 30 that pump the seawater into the vessel 12.

Since the vessel is connected to the flowline that carries the totalfield production, each corresponding well can be completed normally witha Christmas tree. Therefore, PVT samples, logging, well testing, orartificial lift methods can be applied normally, and are not affected bythe vessel.

A method of installing and operating the technology will now bedescribed. Initially, as shown in FIG. 5, the vessel 12 can be towed bya ship 24 on the sea surface to the desired location. Then, the vessel12 is tilted as shown in FIG. 6, and seawater is allowed to fill thevessel 12 until the vessel 12 is partially submerged (FIG. 7). Theseawater that enters the bottom of the vessel 12 by passing through anumber of open sinks 26, which can optionally be equipped with wiremeshes for basic filtration. The air trapped at the top of the vessel12, however, prevents the vessel 12 from sinking. That air can then bereleased from the top of the vessel 12, as shown in FIG. 8, therebylowering the vessel 12 to the desired depth. In some embodiments, aspecific volume of air should remain at the top of the vessel 12 at thisstage. The vessel 12 is then fixed to the seabed by pillars 22, as shownin FIG. 9, and at the same time can be secured to the sea floor usingcables 26 (FIG. 10), as well as to several air-filled spheres 28 (FIG.11), which help to support the vessel 12. Thereafter, the flowline (orproduction manifold) at the seabed can be connected to the pipe 10 atthe bottom of the vessel 12. At the same time, as shown in FIG. 12,pipelines 20 can be connected to the vessel 12 to carry gas 14, oil 16,and other produced fluids 18 away from the vessel 12, such as, forexample, to an onshore site, and pumps 30 can be attached to the vessel12.

As shown in FIG. 13, when the vessel 12 is fixed to its place, and allflowlines and pipelines 20 are connected to it, seawater can be pumpedthrough pumps 30 on the side of the vessel, or otherwise allowed intothe vessel, while the valve at the top of the vessel is opened to allowair to escape. The pumps can continue to inject filtered seawater intothe vessel 12 until the air trapped at the top of the vessel is fullydisplaced by the injected seawater, as shown in FIG. 14. Thereafter,field production is released at the bottom of the seawater filled vessel12, as shown in FIG. 15. Buoyancy elevates crude oil from the bottom ofthe vessel towards the top, as shown in FIG. 16. As oil rises upward,its pressure decreases (due to reduction in hydrostatic pressure), andgas evolves after pressure falls below the bubble point, as shown inFIGS. 17-19. The gas, then, travels upward faster than the oil, due toits lower density. To avoid over pressurizing the vessel, the wateroccupying the lower part of the vessel 12 can be evacuated from thevessel 12 via the pipeline 20 attached to the portion of the vessel 12adjacent the water. In addition, air can be released from an upperportion of the vessel to evacuate the air from the vessel. This step canbe advantageous to assure that no oil or gas contacts oxygen in the air,as this could present a fire hazard. As a result of the evacuation ofwater from the vessel 12, the vessel 12 pressure will decline, allowingfor more gas to separate from oil. After a while, a distinct OWL and GOLforms (as shown, for example, in FIG. 2). When a desired amount of oilor gas is separated and becomes available in the vessel 12, filteredseawater can be injected at the sides of the vessel to pressurize theseparated oil and gas. Thereafter, opening a valve (not shown) to apipeline 20 associated with the oil or gas results in producingpressurized flow oil or gas.

When oil enters the vessel it can experience temperature and pressuredrops. Pressure drops can be controlled by injecting additional seawaterinto the vessel through the seawater injection pumps 30. Temperature,however, can be more difficult to control. In some instances, despitethat the fact that the vessel 12 can be insulated, and can potentiallybe heated, temperature reduction can still occur. The result of suchtemperature reduction is that, at the lower portion of the vessel 12,resins and asphaltenes can precipitate and collect at the bottom of thevessel 12, as shown in FIG. 20. Accordingly, a scraper 32 can beprovided to scrape the bottom of the vessel 12 and collect the resinsand asphaltenes. On the other hand, as crude oil elevates in the vessel12, the pressure exerted by the weight of the fluid column reduces. Whenthis pressure reduction is enough to bring the crude oil pressure belowthe bubble point, gas evolves from the oil. Since gas has the lowestdensity of all the components in the vessel 12, it moves upward fasterthan the other components. Thus, it is possible, due to the combinedeffects of lower overhead pressure gas lift, that resins and asphaltenescould be suspended in the oil zone.

In certain situations, it may not be practical or economical toimplement a full-scale vessel. In such a situation, a smaller scalevessel can be built, as shown, for example, in FIG. 21. Even though theriser pressure drop saved utilizing a smaller vessel is lower than afull-scale vessel, the natural separation of oil and gas can still beaccomplished. Accordingly, a smaller vessel works according to the sameprinciples of the full scale vessel.

The technology herein disclosed helps to resolve certain technicalproblems associated with subsea oil production. One of those problems ispressure drop in risers. As oil travels through a riser, gravitationaland frictional forces can cause the crude oil to lose pressure in theriser. This pressure loss increases when the crude oil pressure fallsbelow the bubble point, which changes the flow from a single-phase to a2-phase (oil and gas) flow. Another problem resolved by the presenttechnology is the need with current technology to invest in multiphasepumps to ship crude oil from platforms to onshore gas oil separationplants (GOSPs). Typically, after the crude oil reaches the platform,through risers, multiphase pumps are used to ship crude oil to a GOSPonshore. Some platforms are equipped with a GOSP, which separates oiland gas, but the oil loses pressure in the process. This results in alarger investment in oil pumps and in gas compressors. The presenttechnology resolves both of these technical problems by providing adevice that both eliminates the need for risers, and that naturallyseparates the oil from the gas. In addition, this technology can be usedat any stage of the field life of a well, including the abandonmentphase.

Models and Experiments

As an example, and to illustrate the effect of utilizing a vessel likethat of the above-described embodiments, a reservoir model was builtassuming production through risers (model 1). In addition, 2 additionalmodels were built assuming production through the proposed vessel (model2, and 3). The parameters of the three models are the same except forvariation in minimum flowing bottom-hole pressure (FBHP) of the oil wellassociated with each model. In model 1, the minimum FBHP was set toabout 5,500 psi. Pressure drop in risers varies significantly withreservoir water depth and production stage. Therefore, two reasonablepressure drop values were considered. In model 2, the wellbore pressuredrop due to the pressure drop in the riser was assumed to be about 1,000psi. Therefore, FBHP was equal to about 4,500 psi in model 2. In modelthree, the wellbore pressure drop due to the pressure drop in the riserwas assumed to be about 2,000 psi. Therefore, FBHP was equal to about3,500 psi in model 3.

All models share the following properties and parameters:

-   -   2 Dimensional model    -   10×10 cells    -   Each cell is 2,500 ft×2,500 ft    -   Thickness=400 ft    -   Depth=12,000 ft    -   Initial Reservoir Pressure=9,000 psi    -   Bubble Point Pressure=4,000 psi    -   Porosity=25%    -   Horizontal Permeability=300 mD    -   Vertical Permeability=50 mD    -   The following PVT properties were used:

P Rs Bo z viso visg 14.7 0 1 0.9999 1.2 0.0125 400 165 1.012 0.8369 1.170.013 800 335 1.0255 0.837 1.14 0.0135 1200 500 1.038 0.8341 1.11 0.0141600 665 1.051 0.8341 1.08 0.0145 2000 828 1.063 0.837 1.06 0.015 2400985 1.075 0.8341 1.03 0.0155 2800 1130 1.087 0.8341 1 0.016 3200 12701.0985 0.8398 0.98 0.0165 3600 1390 1.11 0.8299 0.95 0.017 4000 15001.12 0.83 0.94 0.0175 9000 1510 1.121 0.8301 0.93 0.0176

-   -   Oil density=44.986    -   Gas gravity=0.92    -   The following relative permeability and capillary pressure        values were used:

SWT Sw krw krow Pcow 0.15109 0 1 400 0.180306 7.82404e−007 0.99059227.3408 0.194914 6.62563e−006 0.983136 22.9409 0.22413  1.8312e−0050.964242 18.3843 0.253346 3.68251e−005 0.943733 15.5504 0.2825620.000105562 0.909425 14.3728 0.304915 0.000163382 0.883175 13.47190.326386 0.00021892 0.857961 12.6066 0.347104 0.000272509 0.8059818.59783 0.37021 0.0230609 0.565222 0 0.375229 0.0293539 0.498658 00.403355 0.0713724 0.171756 0 0.43148 0.0868187 0.128584 0 0.4596060.103824 0.0971953 0 0.487732 0.122245 0.0720211 0 0.51629 0.142380.0517967 0 0.545506 0.16506 0.0377328 0 0.574722 0.188013 0.0241556 00.603938 0.213077 0.015662 0 0.633154 0.239975 0.010302 0 0.6564850.261489 0.00636467 0 0.676978 0.282264 0.00437906 0 0.698674 0.3043010.00268985 0 0.720802 0.327792 0.0014622 0 0.740862 0.350697 0.001141850 0.768988 0.382816 0.000692688 0 0.797113 0.414936 0.000243525 00.825239 0.442781  1.5985e−005 0 0.853364 0.46639 7.99251e−006 0 0.881490.49 0 0

SLT Sl krg krog Pcog 0.15109 1 0 3.9 0.168068 0.978622 0 3.854390.202025 0.935866 0 3.76318 0.231981 0.898146 0 3.68271 0.2529590.871731 0 3.62636 0.280516 0.837034 0 3.55234 0.303894 0.796908 03.48053 0.32905 0.721718 0 3.35475 0.354828 0.641161 0 3.22586 0.3775850.570047 0 3.11208 0.405763 0.499134 0 2.97118 0.426119 0.479104 02.8694 0.458476 0.453219 0 2.70762 0.490832 0.427334 0 2.54584 0.524610.400312 0 2.37695 0.555545 0.375564 0 2.22228 0.575545 0.359564 02.12227 0.60408 0.335921 0.000815925 1.97961 0.62648 0.31352 0.005295941.8676 0.648 0.292 0.00960004 1.76 0.672 0.268 0.0144 1.64 0.6960.243687 0.0192 1.52 0.72 0.212 0.0360001 1.4 0.745327 0.1765420.0562617 1.27337 0.768 0.1448 0.0744 1.16 0.792 0.1112 0.0935999 1.040.816 0.08752 0.1368 0.92 0.84 0.0688 0.192 0.800003 0.864174 0.0499440.2476 0.67913 0.888 0.03136 0.3024 0.560002 0.915109 0.0164601 0.3979910.424457 0.936 0.00880006 0.492 0.32 0.96 0 0.6 0.200001 0.976 00.759999 0.120001 1 0 1 0

The reservoir produced from 17 oil wells: 10 horizontal wells and 7vertical wells. Initially, all horizontal producers operated under aconstant maximum flow rate of about 5,000 STB/D, and all verticalproducers operated under constant maximum flow rate of about 2,000STB/D. When the oil operators could not sustain their correspondingmaximum flow rate, they switched to the minimum allowable FBHP (thevalue depends on each model, as described earlier).

The reservoir had 5 horizontal water injectors (for pressure support),operating under maximum 10,000 STBW/D injection rate. A two dimensionalrepresentation of the reservoir model is presented in FIG. 22, and a 3-Dmodel is presented in FIG. 23.

The total reservoir production rate (STB/D) for each model over 10 yearsis presented in FIG. 24, and the cumulative production is presented inFIG. 25. As shown in the charts of FIGS. 24 and 25, the increase incumulative oil produced from the base case (model 1) to the case withlowest FBHP (model 3) is 41%. Notably, as risers increase in length (thedistance from sea surface to seabed) their pressure drop increases aswell. Therefore, when the proposed vessel is employed, therebyeliminating the riser pressure drop, an oil producer can produce under alower FBHP (related to the riser pressure drop through nodal analysis).Lowering the FBHP in the oil wells results in higher flow rates, therebyincreased recovery.

Although the technology herein has been described with reference toparticular embodiments and experimental examples, it is to be understoodthat these embodiments are merely illustrative of the principles andapplications of the present technology. It is therefore to be understoodthat numerous modifications can be made to the illustrative embodimentsand that other arrangements can be devised without departing from thespirit and scope of the present technology as defined by the appendedclaims.

What is claimed is:
 1. A method of installing a gas and oil productionvessel at an offshore well site, the method comprising: a) towing thevessel to a well site with a ship; b) tilting the vessel into an uprightposition, with the top of the vessel oriented above the bottom of thevessel; c) partially filling the vessel with seawater until the vesselis partially submerged; d) fixing the vessel to the seabed using pillarsor cables, or a combination of pillars and cables; e) connecting a pipefrom the well to the bottom of the vessel to deliver field production tothe vessel; f) connecting production pipes at predetermined locations onthe vessel for flowing oil and gas away from the vessel; g) connectingpumps to the vessel to pump seawater into the vessel for purposes ofpressurizing the vessel.
 2. The method of claim 1, further comprisingthe step of: releasing air from an upper portion of the vessel asseawater enters the vessel.
 3. The method of claim 1, filtering theseawater as it enters the vessel to prevent contaminates from enteringthe vessel.
 4. The method of claim 1, further comprising: attachingair-filled spheres to the vessel using cables, the air-filled spheresdesigned to float on the sea surface to help support the vessel.
 5. Themethod of claim 1, further comprising: after step g), pumping seawaterinto the vessel to evacuate remaining air from the vessel, and topressurize the oil and gas within the vessel.